The present invention relates to an optical disc player which emits a beam light to focus on a signal recording surface of an optical disc, detects the light beam reflected on the disc, generates an electrical signal when the reflected beam light is detected, and adjusts a focused position of the light beam incident on the disc through a focus control mechanism of the optical disc player having focusing control means.
In an optical disc player which reproduces a signal recorded on a recording track of the optical disc which is formed of a signal recording surface by the use of a laser beam and/or records information by the use of the laser beam on the optical disc, a focus servo control is carried out to rotate the optical disc and to bring the laser beam to fall on the rotating signal recording surface of the optical disc in an appropriately focused state. The focus servo control is carried out with the focus servo control mechanism. The focus servo control mechanism, e.g., controls a position of an objective lens through which the laser beam focuses on the signal recording surface of the optical disc in a direction orthogonal to the signal recording surface of the optical disc so that a distance from the objective lens to the signal recording surface is adjusted, thus the focused position of the laser beam being placed and held appropriately on the signal recording surface of the optical disc.
In the above-described optical disc player, it is necessary to place the objective lens within a range of a predetermined distance therefrom to the signal recording surface of the optical disc and to place the focused position of the laser beam incidient on the optical disc within a predetermined focusing range with respect to the signal recording surface of the optical disc immediately before the focus servo control is made in order to achieve an accurate focus servo control.
To establish a condition required for starting such an appropriate focus servo control the focus control mechanism of the optical disc player is provided with focusing control means. The focusing control means carries out a focusing operation such that the focused position of the laser beam incident on the optical disc is brought in so-called a just focused state, i.e., the focus is just on the signal recording surface of the optical disc or placed in a state relatively approximate to the just focused state, i.e., placed within the predetermined focusing range with respect to the signal recording surface of the optical disc. Thereafter, the focus servo control is followed.
However, since an operation mode transfer from the focusing operation state to the focus servo control state is carried out on the basis of a result of the reflected beam light, e.g., laser beam derived from the reflection of the laser beam incident on the optical disc, the transfer to the focus servo control mode is carried out with the focused position of the laser beam incident on the optical disc being not placed in the predetermined range with respect to the signal recording surface, in a case when a writable optical disc is used in which an user can record a signal optically on the recording surface and in which a land portion in a spiral form, having a relatively high light reflectivity and a groove portion in a spiral form, having a relatively low light reflectivity, and which is sandwiched between the mutually adjacent land portion are formed and a bottom surface of the groove portion is used as the signal recording surface. Otherwise, the transfer to the focus servo control mode is not carried out even though the focused position of the laser beam is placed in the predetermined focusing range.
In more details, if the above-described writable optical disc is used, a difference in the light reflectivity between the signal recording surface with respect to the incident laser beam and a transparent substrate on an outer surface of which the signal recording surface is formed or an outer surface of a transparent protection layer covering the substrate becomes minor. Therefore, during the focusing operation by means of the above-described focusing control means, it is difficult to determine whether the incident laser beam focuses on the outer surface of the transparent protection layer incident beam side or focuses on the signal recording surface of the optical disc. As a result of this, when the focused position of the incident laser beam is placed within a predetermined distance range with the outer surface of the optical disc at the incident side as a center, the transfer to the focus servo control mode is carried out with the incorrect determination of the focused position. Otherwise, if the optical disc player is set to avoid such an erroneous condition as described above, the player does not detect that the focused position of the incident laser beam is placed in its appropriately focused range and consequently does not carry out the transfer from the focusing mode to the focus servo control mode.